Currently, wireless communications systems find application in many contexts involving the transfer of information transfer from one point to another, and there exists a wide range of modalities suited to meet the particular needs of each. These systems include cellular telephones and two-way radios for distant voice communications, as well as shorter-range data networks for computer systems, among many others. Generally, wireless communications involve a radio frequency (RF) carrier signal that is modulated to represent data and the modulation, transmission, receipt and demodulation of the signal conforming to a set of standards. For wireless data networks, example standards include Wireless LAN (IEEE 802.11), Bluetooth (IEEE 802.15.1), and ZigBee (IEEE 802.15.4), which are generally time domain duplex systems where a bidirectional link is emulated on a time divided communications channel.
A fundamental component of a wireless communications system is the transceiver which includes the transmitter and receiver circuitry. The transceiver, with its digital baseband subsystem, encodes the digital data to a baseband signal and modulates the baseband signal with an RF carrier signal. The modulation utilized for WLAN includes orthogonal frequency division multiplexing (OFDM), quadrature phase shift keying (QPSK) and quadrature amplitude modulation (16 QAM, 64 QAM); for Bluetooth includes GFSK and 4/8-DQPSK; and for Zigbee includes BPSK and OQPSK (or MSK).
Upon receipt of the signal from the antenna, the transceiver downconverts the RF signal, demodulates the baseband signal and decodes the digital data represented by the baseband signal. The antenna connected to the transceiver converts the electrical signal to electromagnetic waves, and vice versa. Depending upon the particular configuration, the transceiver may include a dedicated transmit (TX) line and a dedicated receive (RX) line or the transceiver may have a combined transmit/receive line. In the case of separate TX and RX lines, the transmit line and the receive line are typically tied to a single antenna, particularly for low-cost and/or small-size applications.
The circuitry between the transceiver and the antenna is commonly referred to as the front end module (FEM). The FEM includes an RF power amplifier (PA) which generates output transmit signals by amplifying weaker input signals in wireless devices, such as cellular telephone handsets. Many of these communication devices are configured to operate in different frequency bands for different communication systems. For example, third generation (3G) cellular communication systems, 4G cellular (LTE) systems, 802.11 WLAN systems, etc.
An additional component in the signal chain is the transmit/receive (TX/RX) switch which functions to direct the high power transmit signal to the antenna and also prevents that signal from entering the sensitive front end of the local receiver, while allowing a low-loss connection between the antenna and the receiver. The TX/RX switch may be integrated into the FEM or as a standalone component.
It is therefore desirable to have a TX/RX switch capable of directing power to the antenna and also preventing the signal from entering the receiver while providing a low loss connection between the antenna and receiver. In it also desirable to have a TX/RX switch that meets the performance requirements of modern wireless standards such as 802.11, 3G and 4G cellular systems while reducing manufacturing complexities, size and cost.